A conventional method of manufacturing solid capacitors is described next with reference to drawings. FIG. 5 shows a perspective, partly in section, illustrating the configuration of a solid capacitor. In FIG. 5, after the surface of an aluminum foil 1, which acts as the anode (positive electrode), is roughened by etching, an anodized film is formed on the surface of the roughened aluminum foil 1 through anodization. An insulative resist 11 separates the aluminum foil 1 into an anode and cathode (negative electrode). The cathode is made by sequentially laminating a MnO.sub.2 layer 12, polypyrrole layer 13 which becomes the conducting polymer layer, graphite layer 14, and silver paint layer 15. A solid capacitor element is configured as described above.
A single or multi-laminated solid capacitor element as configured above is molded with a packaging resin 17 (not illustrated) after terminal members 16A and 16B are connected to the anode and cathode. This completes the solid capacitor.
In the conventional method of manufacturing solid capacitors as above, the aluminum foil 1, the initial material, is generally provided in the form of a strip of predetermined length wound around a reel. The aluminum foil 1 wound around one reel is considered as one lot, and is successively supplied to the above series of processes. Accordingly, if the characteristics of the aluminum foil vary significantly in the processes relatively close to raw materials, the product yield may drop in the conventional manufacturing method.
More specifically, during the process of forming the MnO.sub.2 layer 12 on an anodized film of the aluminum foil 1 in FIG. 5, a strip of the aluminum foil 1 is successively immersed in and removed from a solution containing manganese salts. The manganese salt is then thermally decomposed to form the MnO.sub.2 layer 12 on the surface. This process has a marked detrimental effect on the anodized film already formed on the aluminum foil 1, often resulting in damage to some parts of the anodized film.
Accordingly, another anodization step is implemented after the MnO.sub.2 layer formation process in order to repair the damaged anodized film. However, this repair process is not always sufficient. Considering the degradation in characteristics of the anodized film on an aluminum foil (hereinafter referred as characteristics of the aluminum foil) 1 during the MnO.sub.2 layer formation process, the entire lot of aluminum foil 1 rolled on the reel may not be reliably input to the following MnO.sub.2 layer formation process.
The present invention aims to offer a method of manufacturing solid electrolytic capacitors that allows the reliable input of the entire lot of aluminum foil, on which an anodized film is formed, to the MnO.sub.2 layer formation process, and also to improves the product yield.